In the conveyer system of continuously producing aluminium cans, glass bottles, PET bottles and others, conveyer chains are much used as the means of conveyance of such objects. This system of using conveyer chains includes the steps of stopping the stream of the objects being conveyed and drawing up them in order in the middle of the conveyance thereof, in which the objects must be slid on the conveyer chain relatively thereto in such steps of stopping the stream of the objects and drawing up them in order.
One example of promoting the slidability of the outer surface of such a conveyer chain is to employ chains made of resins. Heretofore, polyoxymethylene resins, polyetherimide resins or fluorine-containing resins have been used as the materials of the links for resin chains of conveyers. However, such plastic links are greatly worn away, as having poor hardness, and their life is therefore short. If graphite is added to such plastic links in order to enhance their hardness, their kinetic friction coefficient is lowered. However, the graphite added drops out due to friction to produce dust, which is problematic in that the dust is incorporated into the inside and the surface coats of the objects being conveyed to thereby worsen the quality of the objects and that the dust has some negative influences on the electronic circuits in the adjacent devices.
In practical conveyer system lines, a lubricant such as water or soapy water is applied onto the outer surfaces of conveyer chains to thereby promote their slidability. In general, however, since the outer surfaces of conventional conveyer chains on which objects are conveyed are flat (see Japanese Utility Model Application Laid-Open No. 57-49812), objects are conveyed thereon with their bottom surfaces being tightly attached on the outer surfaces of the conveyer chains. Accordingly, even if such a lubricant is applied onto the outer surfaces of the conveyer chains in order to promote their slidability, the lubricant is stripped off from the outer surfaces of the conveyer chains by the bottom surfaces of the objects being conveyed thereon, resulting in that the slidability of the outer surfaces of the conveyer chains is still insufficient.
If relatively hard, fine impurities, such as glass powder or metal powder, adhere to the outer surfaces of conveyer chains, such causes another problem in that the bottom surfaces of objects being conveyed on the conveyer chains are scratched by the fine impurities.
Therefore, the object of the present invention is to provide a conveyer chain capable of promoting the slidability of its outer surface on which objects are conveyed while reducing the damage of the bottom surfaces of the objects being slid.